Wear-resistant, superabrasive cutting elements are currently used in rotary drill bits for drilling a borehole in a subterranean formation. Polycrystalline diamond compacts (“PDCs”) have found particular utility as superabrasive cutting elements for such rotary drill bits. FIGS. 1 and 2 are isometric and top elevation views, respectively, of a prior art rotary drill bit 100 that utilizes a plurality of PDCs as cutting elements. The rotary drill bit 100 comprises a bit body 102 that includes radially- and longitudinally-extending blades 104 having leading faces 106. The bit body 102 further includes a threaded pin connection 108 for connecting the bit body 102 to a drilling string. Circumferentially adjacent blades 104 define so-called junk slots 109 therebetween. The bit body 102 defines a leading end structure for drilling into a subterranean formation by rotation of the bit body 102 about a longitudinal axis 110 and application of weight-on-bit. The bit body 102 also may include a plurality of nozzle cavities 111 for communicating drilling fluid from the interior of the bit body 102 to a plurality of fixed cutting elements 112 during drilling.
As best shown in FIG. 2, each of the cutting elements 112 may be secured to one of the blades 104. Each of the cutting elements 112 may include a polycrystalline diamond (“PCD”) table 114 bonded to a substrate 116 (e.g., a cemented tungsten carbide substrate). For example, each of the cutting elements 112 may be attached to one of the blades 104 by brazing or press-fitting the substrate 116 of each of the cutting elements 112 to a corresponding blade 104 (e.g., within corresponding cutter pockets formed within each blade 104).
Due to the cutting elements 112 being attached to the bit body 102, only a portion of each cutting element 112 is subjected to extensive abrasive wear during drilling. FIG. 3 is a partial, side cross-sectional view depicting wear of one of the cutting elements 112 during drilling. As shown in FIG. 3, the cutting element 112 bears against and penetrates a subterranean formation 300 during drilling. Only a portion of a circumferential cutting edge 302 of each cutting element 112 is subjected to extensive abrasive wear during drilling. The cutting effectiveness of the cutting elements 112 substantially diminishes as a result of the localized wear of the circumferential cutting edge 302. This localized wear can necessitate replacing or rotating the cutting elements 112 despite most of the PCD tables 114 of the cutting elements 112 being relatively unaffected by the drilling. Alternatively, wear may extend into the substrate 116, which may also necessitate replacement of the cutting elements 112.
A number of different types of passive, rotatable cutting elements have been designed to purportedly attempt to reduce localized wear of a cutting element during drilling. Typically, such rotatable cutting elements including a PDC received by and rotatable within a housing that is attached to a bit body of a rotary drill bit. During drilling, the PDCs can rotate so that wear thereof may not be as localized as with a fixed cutting element, such as the cutting elements 112 shown in FIGS. 1-3. However, unpredictability of the nature of contact between a rotatable PDC and a subterranean formation being drilled, extreme temperatures, forces, and pressures encountered in subterranean drilling environments may prevent or at least inhibit rotation of a conventional rotatable PDC. Thus, such conventional rotatable PDCs, as with fixed cutting elements, may exhibit a circumferential cutting edge that still locally degrades and wears down, resulting in decreased operational lifetime and drilling efficiency.
Therefore, there is still a need in the art for a cutting element for use in a rotary drill bit that more uniformly wears during use and, consequently, exhibits an increased operational lifetime.